This invention relates in general to radio frequency antennas and, more specifically, to an improved, high efficiency, low cost end fed half wave folded dipole antenna.
A wide variety of antennas have been developed for use in sending and receiving radio signals. These range from a very simple long wire antenna to very small electronically complex antennas. Antennas are generally optimized for the frequency range to be used and the particular type of transmissions involved.
Recently, there has been increased interest in small, low cost antennas for applications such as cellular telephones, alarm systems and the like. Alarm systems that automatically transmit an alarm signal in such circumstances as a breaking and entry, triggered by a person having a medical emergency, or in response to other problems so that an appropriate response can be made from a central station are coming into greater use. Since a multiplicity of sensors may each have its own signal transmission system, it is important that the system and associated antenna be both inexpensive and efficient.
Simple, fractional wave length, e.g. half wave, antennas are often used. However, these antennas are difficult to precisely tune to a desired wavelength and do not have optimum gain and frequency response.
More complex small antennas are widely used in cellular telephone systems. Typical of these are the antennas described by Sheriff in U.S. Pat. No. 4,975,713. While very compact and effective, they are generally more complex and expensive than would be desirable in a multi-antenna alarm system.
Thus, there is a continuing need for small compact antennas of increased performance and lower cost for use in applications such as alarm systems.